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A modification of the Adler capillary assay was used to evaluate the chemotactic responses of several denitrifiers to nitrate and nitrite. Strong positive chemotaxis was observed to NO3− and NO2− by soil isolates of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Pseudomonas stutzeri, with the peak response occurring at 10−3 M for both attractants. In addition, a strong chemoattraction to serine (peak response at 10−2 M), tryptone, and a soil extract, but not to NH4+, was observed for all denitrifiers tested. Chemotaxis was not dependent on a previous growth on NO3−, NO2−, or a soil extract, and the chemoattraction to NO3− occurred when the bacteria were grown aerobically or anaerobically. However, the best response to NO3− was usually observed when the cells were grown aerobically with 10 mM NO3− in the growth medium. Capillary tubes containing 10−3 M NO3− submerged into soil-water mixtures elicited a significant chemotactic response to NO3− by the indigenous soil microflora, the majority of which were Pseudomonas spp. A chemotactic strain of P. fluorescens also was shown to survive significantly better in aerobic and anaerobic soils than was a nonmotile strain of the same species. Both strains had equal growth rates in liquid cultures. Thus, chemotaxis may be one mechanism by which denitrifiers successfully compete for available NO3− and NO2−, and which may facilitate the survival of naturally occurring populations of some denitrifiers. 相似文献
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Summary The effect of the exchangeable cation on the condensation of glycine and alanine was investigated using a series of homoionic bentonites. A cycling procedure of drying, warming and wetting was employed. Peptide bond formation was observed, and the effectiveness of metal ions to catalyze the condensation was Cu2+ > Ni2+ Zn2+ > Na+. Glycine showed 6% of the monomer incorporated into oligomers with the largest detected being the pentamer. Alanine showed less peptide bond formation (a maximum of 2%) and only the dimer was observed. 相似文献
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James B. Orenberg Kristi M. Kjos Reva Winkler Joseph Link James G. Lawless 《Journal of molecular evolution》1982,18(2):137-143
Summary The interactions of Ni(II) cation with a representative suite of purine bases and the respective nucleosides and nucleotides have been studied by ultraviolet difference spectroscopy. Apparent association constants, Kapp, were determined for each system at pH 7.0, using computer linear regression coupled with an iteration technique. The specificity of binding of Ni2+ for the purine nucleotides studied at pH 7.0 was 5-GMP > 5-IMP > 5-AMP; a similiar ordering was also found for the respective nucleosides and bases. In this study binding was not observed for the suite of pyramidines used, although a Ni2+ - cytidine complex has been observed (Fiskin and Beer, 1965). It was also found that Ni2+ bound more strongly to the purine 5-nucleotides than to the respective nucleosides and bases. These trends are explained in terms of metal-ligand bonds and available bonding positions on the ligands. A role for metal-ion-nucleotide types of complexes is suggested in the processes that might have given rise to the origin of life. 相似文献
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J?Craig CohenEmail author Lennart?KA?Lundblad Jason?HT?Bates Michael?Levitzky Janet?E?Larson 《BMC genetics》2004,5(1):21